Basic Requirements of Lead-free Electronic Solder for Electronic Assembly (Part I)
The basic processes of lead-free welding assembly include: a. Lead-free PCB manufacturing process; B. 96.5Sn/3.5Ag and 95.5Sn/4.0Ag/0.5Cu eutectic and near eutectic alloy systems used in solder paste; C. 99.3Sn/0.7Cu eutectic alloy system for wave soldering applications; D. 99.3Sn/0.7Cu alloy system for manual soldering.
Although these are all feasible processes, there are still several major problems to be solved. For example, the cost of raw materials for electronic solder is still higher than standard Sn/Pb process, the restriction of wettability is increased, the requirement of keeping inert air in wave soldering process (with sufficient nitrogen) and the possibility of raising reflow soldering temperature to the limit temperature range (between 235 and 245 C) to improve the performance of various components. Thermal requirements and so on.
As far as lead-free alternatives for electronic solders are concerned, there is no universally accepted standard. After many discussions with many professionals in this field, we have come to the following technical and application requirements:
Metal prices Many assembly manufacturers require lead-free alloys to be priced no higher than 63Sn/37Pb, but unfortunately all existing lead-free substitutes cost at least 35% more than 63Sn/37Pb. Metal cost is the most important factor in the selection of lead-free solder rods and solder wires, while in the production of solder paste, the price of metal is not so sensitive because of the relatively high proportion of technical cost in the overall manufacturing cost.